The objective of this proposed research is to determine the identity, structure and expression of the herpes simplex viral genes involved in the alteration of cellular growth properties by transformation of the cells. The region of the herpes simplex virus type 1 (HSV-1) genome capable of transformation has been identified, but no viral mutants have been isolated in this viral function. For this reason we propose a detailed genetic study of the transformation region by the directed mutagenesis of this region. We will isolate temperature-sensitive mutants and host-range mutants in this region of the genome. We also plan to isolate new early mutants that regulate the expression of the transforming gene(s). We specifically propose to 1) mutagenize in vitro restriction endonuclease DNA fragments from the transforming region of the genome and re-introduce the DNA fragments into an infectious genome by marker rescue; 2) screen for and characterize temperature-sensitive mutants and host-range mutants; 3) insert DNA sequences from the transforming and early gene regions into new regions of the genome in an attempt to determine how the expression of these gene sequences is regulated. The goal of these studies is to identify each of the viral genes involved in cellular transformation and to assign the precise molecular function of each. The correlation of a defect in the biochemical properties of the proteins encoded by these genes with the lesions introduced will allow the assignment of these functions.